SPN 91 FMI 2Electrical/J1939High
Accelerator Pedal Position — Erratic
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 91 / FMI 2
Category
Electrical/J1939
Fault Type
sensor
FMI Category
data erratic
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: Accelerator pedal position sensor — integrated with accelerator pedal assembly, cab floor
Common Symptoms
- Erratic throttle response
- Engine surging
- Cruise control issues
- Possible derate
- Throttle not responding to pedal input
Root Causes
- Accelerator pedal position sensor failed
- Wiring harness damage to pedal sensor
- Pedal sensor connector corrosion
- ECM input circuit fault
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
Pedal sensor failure common at 300k–500k miles. Connector corrosion from floor moisture.
System Interactions
SPN 91 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: Cummins TSB 4021160 — Accelerator Pedal Position Sensor Diagnosis
Common Diagnostic Mistakes
Replacing the sensor without verifying wiring continuity and supply voltage first.
Clearing codes without identifying and resolving the root cause — the fault will return.
Ignoring related active faults — cascading faults often share a root cause.
Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.
Condemning the ECM before exhausting all wiring and component tests.
OEM Notes
Cummins
X15: Pedal sensor P/N varies by cab. Check connector for moisture.
Detroit
DD15: DDDL shows pedal position %. Check for floor mat interference.
PACCAR
MX-13: Check pedal sensor mounting for looseness.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 91 FMI 2 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.
Authority References
Diagnostic procedures on this page are informed by OEM service literature and industry standards.
Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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